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United States Patent |
5,673,328
|
Wandl
,   et al.
|
September 30, 1997
|
Bone conducting hearing aid
Abstract
A bone conducting hearing aid comprises a housing adapted to be pressed
against a head of a user and a magnetic system held in the hearing aid
housing, The magnetic system includes a permanent magnet, a coil, an
armature of a soft magnetic material and a spring holding the armature. A
conductor button is arranged to move with the armature, the conductor
button being shaped to be brought into contact with the mastoid bone of
the user's head, and a rubber bearing having a predetermined elastic
constant holds a support spring for the conductor button on the hearing
aid housing. To increase the difference between the useful signal and the
spurious signal received by the hearing aid, the support spring has an
elastic constant not exceeding 0.4 N/cm.
Inventors:
|
Wandl; Rudolf (Vienna, AT);
Schermann; Kurt (Oberwart, AT)
|
Assignee:
|
Viennatone GmbH (Vienna, AT)
|
Appl. No.:
|
432762 |
Filed:
|
May 2, 1995 |
Foreign Application Priority Data
Current U.S. Class: |
381/151; 381/312; 381/327 |
Intern'l Class: |
H04R 025/00 |
Field of Search: |
381/151,68.3,68,68.6,68.7,200,68.5,23.1
600/25
|
References Cited
U.S. Patent Documents
Re19808 | Jan., 1936 | Kranz | 381/151.
|
2702354 | Feb., 1955 | Chorpening | 381/151.
|
2832842 | Apr., 1958 | Knauert | 381/151.
|
Primary Examiner: Le; Huyen
Attorney, Agent or Firm: Burns, Doane, Swecker & Mathis, LLP
Parent Case Text
This is a continuation of application Ser. No. 08/127,823 filed on Sep. 27,
1993, now abandoned.
Claims
What is claimed is:
1. A bone conducting hearing aid incorporated in an eyeglass frame,
comprising
(a) a housing adapted to be pressed against a head of a user,
(b) a magnetic system held in the hearing aid housing, the magnetic system
including
(1) a permanent magnet,
(2) a coil,
(3) an armature of a soft magnetic material and
(4) a spring holding the armature,
(c) a conductor button arranged to move with the armature, the conductor
button being shaped to be brought into contact with the mastoid bone of
the user's head,
(d) a support made of an elastically deformable material, having a
predetermined elastic constant and
(e) a support spring for the conductor button, said elastically deformable
support positioned between the housing and the support spring; said
support holding the support spring on the hearing aid housing and the
support spring having an elastic constant not exceeding 0.4 N/cm.
2. The bone conducting hearing aid of claim 1 wherein the conductor button
transmits a useful signal, wherein a spurious signal is transmitted from
the housing, and the spring constant of the support spring causes at least
a maximum separation between the useful signal and the spurious signal of
at least 10 db.
3. The bone conducting hearing aid of claim 1 wherein the conductor button
transmits a useful signal, wherein a spurious signal is transmitted from
the housing, and wherein the useful signal exceeds the spurious signal
over a frequency range extending from about 100 Hz to in excess of 10,000
Hz.
4. A bone conducting hearing aid incorporated in an eyeglass frame,
comprising:
(a) a housing adapted to be pressed against a head of a user;
(b) a magnetic system held in the hearing aid housing, the magnetic system
including
(1) a permanent magnet;
(2) a coil;
(3) an armature of a soft magnetic material and
(4) a spring holding the armature,
(c) a conductor button arranged to move with the armature, the conductor
button being shaped to be brought into contact with the mastoid bone of
the user's head;
(d) a support made of an elastically deformable material, having a
predetermined elastic constant and
(e) a support spring for the conductor button, said elastically deformable
support positioned between the housing and the support spring; said
support holding the support spring on the hearing aid housing and the
support spring having an elastic constant not exceeding 0.4 N/cm; and
wherein the elastic constants of the support and the support spring are
substantially equal.
5. The bone conducting hearing aid of claim 4, wherein the elastically
deformable material is rubber.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a bone conducting hearing aid comprising a
housing adapted to be pressed against a head of a user, a magnetic system
held in the hearing aid housing, the magnetic system including a permanent
magnet, a coil, an armature of a soft magnetic material and a spring
holding the armature, and a conductor button arranged to move with the
armature, the conductor button being shaped to be brought into contact
with the mastoid bone of the user's head. A support made of an elastically
deformable material, e.g. rubbers having a predetermined elastic constant
holds a support spring for the conductor button on the hearing aid housing
and serves to uncouple the support spring. The hearing aid housing may be
incorporated in an eyeglass frame.
2. Description of the Prior Art
Such a bone conducting hearing aid is known and shown schematically in the
fragmentary illustration of FIG. 1. The alternating current signal of an
amplifier (not shown) is transmitted to the terminals oaf the magnetic
system coil, which causes the armature in cooperation with the permanent
magnetic field of the annular permanent magnet to vibrate because of the
modulated magnetic field. These vibrations are transmitted by the
conductor button, which moves with the armature, through the skin and the
underlying layer of fat to the mastoid bone of the user, the required
contact pressure being obtained by a suitable pre-tensioning of the
hearing aid housing against the head of the user and by the support spring
for the conductor button which is shaped to be brought into contact with
the mastoid bone of the user's head. The housing may be incorporated in an
eyeglass frame.
Conventionally, the parts of such a hearing aid have been dimensioned
empirically with a view to obtaining the greatest power transmission to
the mastoid bone with the smallest possible size of the hearing aid in the
sound range to be transmitted. Ideally, the mass of the base with the
built-in magnetic system should be infinitely large to transmit the entire
vibration energy delivered by the armature to the mastoid bone of the user
of the hearing aid. In reality, this mass must be finite and the base of
the built-an magnetic system vibrates in counter-phase to the conductor
button, which causes a portion of the vibration energy to be lost for
transmission. Obviously, with an otherwise unchanged structure, the
effectiveness of such a bone conducting hearing aid can be enhanced only
by increasing the mass of said base with the magnetic system. This, on the
other hand, runs counter to the requirement to make the hearing aid as
slender and light as possible.
The empirical determination of the dimensioning of the hearing aid can be
used only to a limited extent to obtain optimal conditions because of the
multiplicity of the parameters to be influenced and the resultant number
of required tests.
SUMMARY OF THE INVENTION
It is the primary object of this invention to overcome this disadvantage
and to provide a bone conducting hearing aid in which the difference
between the useful signal and the spurious signal is enhanced.
In a bone conducting hearing aid of the first-described structure, this and
other objects are accomplished according to the invention by the use of a
support spring having an elastic constant not exceeding 0.4 Newton per cm
N/cm. Preferably, the elastic constants of the support spring and its
support made of an elastically deformable material are equal.
BRIEF DESCRIPTION OF THE DRAWING
The above and other objects, advantages and features of the present
invention will become more apparent from the following detailed
description of certain preferred embodiments thereof, taken in conjunction
with the accompanying schematic drawing wherein
FIG. 1 is a fragmentary view of a conventional bone conducting hearing aid;
FIG. 2 diagrammatically illustrates a structure of a vibrating system in
simplified form;
FIG. 3 shows a frequency diagram of a conventional hearing aid system; and
FIG. 4 is a like diagram of the hearing aid system according to this
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 diagrammatically shows a conventional bone conducting hearing aid.
Essentially, this hearing aid comprises housing 6 adapted to be pressed
against a head of a user (not shown). The housing may be incorporated in a
conventional eyeglass frame. A magnetic system is held in hearing aid
housing 6 by base 9 and the magnetic system includes annular permanent
magnet 1, coil 2 surrounded by the annular permanent magnet and armature 3
of a soft magnetic material. The annular permanent magnet is mounted on
yoke 12 and spring 4 holds the armature, a small air gap being
conventionally defined between permanent magnet 1 and armature 3.
Conductor button 5 is arranged to move with armature 3 when the same is
vibrated upon excitation of the magnetic system, the conductor button
being shaped to be brought into contact with the mastoid bone of the
user's head (not shown). Support 7 made of an elastically deformable
material like rubber having a predetermined elastic constant holds support
spring 8 for conductor button 5 on the hearing aid housing 6. Base 9 with
the magnetic system is held by armature spring 4 and armature 3 by support
spring 8 and the latter is held on housing 6 by said elastic support 7.
When the user puts on the eyeglasses, its frame will press hearing aid
housing 6 incorporated therein against the head of the user and conductor
button 5 against the mastoid bone.
During use, the output signals from an amplifier (not shown) will be
transmitted to the terminals of coil 1, causing armature 3 to be vibrated
and the vibrations to be transmitted by conductor button 5 through the
skin and the underlying fat layer to the mastoid bone.
The simplified showing of a vibrating system in FIG. 2 illustrates the many
conditions that need to be taken into consideration when to find an
optimal dimensioning of such a hearing aid. In this figure,
m1 indicates the mass of armature 3, together with conductor button 5
connected thereto;
m0 indicates the mass of base 9, together with magnet 1, yoke 12 and coil
2;
mB indicates the mass of head 10 of the user;
mH indicates the mass of hearing aid housing 6; and
f(t) indicates the actual vibration generator or transducer (magnet 1, yoke
12, coil 2 and armature 3) which converts the output of the
non-illustrated amplifier into a mechanical energy.
As FIG. 1 clearly shows, all the above-named masses are interconnected by
elastic elements, each of which may be considered to be constituted by an
ideal spring having an elastic constant k and a damping force C. The index
H designates skin and fat layer 11 of the head of the user between
conductor button 5 and the user's mastoid bone, index T designates
armature spring 4, index D1 support spring 8 and index D2 elastic support
7 for support spring 8.
In a well constructed and dimensioned hearing aid of this type, as much
energy as possible should be transmitted from mass m1, which is comprised
of armature 3 and conductor button 5, to mass mB, which is comprised of
the user's head, through signal path A, in which lies the skin and fat
layer 11 of the user, to obtain a high efficiency. On the other hand, as
little energy as possible should be transmitted by mass m1 to mass mH,
which is constituted by housing 6, through signal path B, which is
constituted by support spring 8 and elastic support 7, to avoid
co-vibration of housing 6 and its built-in microphone (not shown).
For an optimal transmission through signal path A, there is a connection
between elastic constant kH of skin and fat layer 11, which may be
statically determined, and elastic constant kT of armature spring 4. To
obtain a proper sound insulation of hearing aid housing 6, i.e. the temple
of an eyeglass frame, an optimal relation between elastic constant kT of
armature spring 4, kD1 of support spring 8 and kD2 of elastic support 7
for the support spring must be attained.
To obtain a predetermined relationship between mass m1 of armature 3 with
conductor button 5 and mass m0 of base 9, with magnet 1, yoke 12 and coil
2, different pairs of elastic constants must be paired. Depending on the
structure of the masses, spring and damping forces, a vibration frequency
range will be amplified or damped. The transmittable frequency range can
be increased and the efficiency may be enhanced by a suitable selection of
these parameters. The characteristic for this selection is elastic
constant kD1 of support spring 8 and elastic constant kD2 of elastic
support 7 for support spring 8.
To obtain as stable a hearing aid as possible, it has heretofore been
proposed to use as stiff a spring as possible for support spring 8, i.e. a
spring having an elastic constant exceeding 0.7 N/cm, and to attempt to
minimize the transmission of spurious noise to housing 6 by the use of a
soft elastic support 7. Such a conventional system has a support spring
whose elastic constant is much larger than that of its elastic support
while damping force CD2 of elastic support 7 is much larger than damping
force CD1 of support spring 8, the latter damping force, in turn, being
much larger than damping force CT of armature spring 4 whose damping force
was chosen to be as close as possible to zero.
As will be noted from FIG. 3 showing a frequency diagram of a
conventionally dimensioned bone conducting hearing aid, the mutual
decoupling of such a system is highly deficient and the transmission of
the spurious signal to housing 6 is almost as great as that of the useful
signal transmitted to the mastoid bone of the user. To avoid feedback, a
very complicated mounting of the non-illustrated microphone in hearing aid
housing 6 has been required. This disadvantage has been overcome if the
elastic constant of support spring 8 does not exceed 0.4 N/cm, in which
case a very distinct difference in the magnitude of the useful and
spurious signals is obtained. Surprisingly, compared to conventional
systems, the distance between the useful signal and the spurious signal
has been improved by about 20 dB.
As shown by a comparison between FIGS. 3 and 4, respectively showing
frequency diagrams of a conventional hearing aid and a hearing aid
according to the invention, if the elastic constant of support spring 8 is
no more than 0.4 N/cm, the useful signal will be considerably enhanced as
compared to conventional systems, the figures showing the curves of the
useful and spurious signals in a conventionally dimensioned hearing aid
and the novel hearing aid. It has been found to be particularly
advantageous if the elastic constants of support spring 8 and rubber
bearing 7 are substantially equal.
The choice of elastic constants according to the present invention makes it
possible to decrease the size and the weight of the hearing aid
considerably, as compared to conventional hearing aids of this type with
the same output efficiency. Furthermore, use may be made of much less
complicated microphone mountings.
The more pronounced wave formation of the vibration frequency curve in the
present hearing aid, which can be gleaned from FIG. 4, has no drawback in
the use of the hearing aid since, to the contrary, the worse low sound
reproduction in the median frequencies contributes to a better hearing in
a noisy environment.
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